The embodiments described herein relate generally to power equipment protection devices and, more particularly, to apparatus that include adjustable electrode assemblies and an ablative plasma gun for use in eliminating arc flashes.
Known electric power circuits and switchgear generally have conductors that are separated by insulation, such as air, or gas or solid dielectrics. However, if the conductors are positioned too closely together, or if a voltage between the conductors exceeds the insulative properties of the insulation between the conductors, an arc can occur. The insulation between the conductors can become ionized, which makes the insulation conductive and enables formation of an arc flash.
An arc flash is caused by a rapid release of energy due to a fault between two phase conductors, between a phase conductor and a neutral conductor, or between a phase conductor and a ground point. Arc flash temperatures can reach or exceed 20,000° C., which can vaporize the conductors and adjacent equipment. Moreover, an arc flash can release significant energy in the form of heat, intense light, pressure waves, and/or sound waves, sufficient to damage the conductors and adjacent equipment. However, the current level of a fault that generates an arc flash is generally less than the current level of a short circuit, such that a circuit breaker may not trip or exhibits a delayed trip unless the circuit breaker is specifically designed to handle an arc fault condition. Although agencies and standards exist to regulate arc flash issues by mandating the use of personal protective clothing and equipment, there is no device established by regulation that eliminates arc flash.
Standard circuit protection devices, such as fuses and circuit breakers, generally do not react quickly enough to mitigate an arc flash. One known circuit protection device that exhibits a sufficiently rapid response is an electrical “crowbar,” which utilizes a mechanical and/or electro-mechanical process by intentionally creating an electrical “short circuit” to divert the electrical energy away from the arc flash point. Such an intentional short circuit fault is then cleared by tripping a fuse or a circuit breaker. However, the intentional short circuit fault created using a crowbar may allow significant levels of current to flow through adjacent electrical equipment, thereby still enabling damage to the equipment.
Another known circuit protection device that exhibits a sufficiently rapid response is an arc containment device, which creates a contained arc to divert the electrical energy away from the arc flash point. Such known devices generally include two or more main electrodes separated by a gap of air. Moreover, each main electrode is threaded directly into a corresponding electrode holder. These electrodes cause electrical energy to concentrate at the interface point with the electrode holder, i.e., at the thread, which creates a structurally weak point that can cause failure during use. Moreover, this concentration of energy at the interface point can cause the electrode to become welded or melted to the electrode holder, which requires replacement of both the electrode and the electrode holder after use. Furthermore, because of tolerances in the manufacture of such threaded electrodes, it can be difficult to position these electrodes to obtain consistent results.
During operation, a bias voltage is applied to the main electrodes across the gap. However, at least some known electric arc devices require the main electrodes to be positioned closely together to obtain desired operation. Contaminants, or even the natural impedance of the air in the gap, can lead to arc formation between the main electrodes at undesirable times, which can lead to a circuit breaker being tripped when it would be otherwise unnecessary. Accordingly, at least some known electric arc devices simply position the main electrodes further apart to avoid such false positive results. However, these devices are typically less reliable because of a less effective spread of plasma from a plasma gun. For example, at least some known plasma guns provide a plasma spread that does not effectively promote effective dielectric breakdown and reduction of impedance in the gap of air between the main electrodes. Such plasma guns can therefore show a lower level of reliability.